AB-rated drugs are drugs that meet the necessary bioequivalence standards established by the Food and Drug Administration (FDA).

A generic drug is considered bioequivalent to a brand-name drug if it contains the same active pharmaceutical ingredient as the branded drug, and if there is no significant difference in the formulation, quality, and effectiveness of the two drugs.

A pharmaceutical company seeking to market a generic version of a branded drug may file an Abbreviated New Drug Application (ANDA) with the FDA. In turn, the FDA will check whether or not the generic version submitted by the company meets the necessary bioequivalence standards. Upon approval, the FDA will rate this generic version as an AB-rated generic drug.

At the pharmacy, generic substitution is the process by which a generic equivalent is dispensed rather than the brand-name drug.

Many third party payers of prescription drugs (e.g., health insurance plans, Medicare and Medicaid programs) have adopted policies to encourage the substitution of the lower-priced AB-rated generic drugs for the higher-priced branded drugs, when an AB-rated generic drug is available.

On the other hand, there are non-AB rated drugs being dispensed by pharmacists every day. The non-AB rated products may not be substituted by the pharmacist without the permission from the doctor, because the non-AB rated drugs are considered therapeutic alternatives and therefore they are not generic substitutes.

If the pharmacist wants to change the patient's prescription to a non-AB rated drug, the pharmacist should get the patient's physician approval for the change. Nevertheless, a lot of pharmacists do not call the doctor to get the approval because calling the doctor to ask permission to dispense a non-AB rated drug depends on the pharmacy policy and on the state government regulation. On the other hand, it is worth noting that most doctors will allow the pharmacist to change the patient's prescription to a non-AB rated drug.

Generally speaking, non-AB rated drugs are drugs first marketed between 1938 and 1962 which were approved as safe, but not required to show effectiveness for FDA product approval.

In other words, there are pharmaceutical companies still manufacturing drugs using ingredients from the 1950's and therefore the pharmaceutical company does not feel obligated to seek approval from the FDA. Nevertheless, the company has to register the non-AB rated drug with the FDA in order to get the NDC number. In addition, the FDA requires that both the AB-rated drugs and the non-AB rated drugs be manufactured in compliance with current good manufacturing practices.

For example, if the doctor writes a prescription for Pyridium 200mg, the pharmacist may dispense the therapeutic alternative to Pyridium, which is Phenazopyridine. But, before dispensing Phenazopyridine 200mg, the pharmacist should call the doctor in order to ask for permission because Phenazopyridine is a non-AB rated drug.

Another example, if the physician writes a prescription for Levsin 0.125mg, the pharmacist may dispense the therapeutic alternative to Levsin, which is Hyoscyamine. But, before dispensing Hyoscyamine 0.125mg, the pharmacist should call the physician in order to ask for permission because Hyoscyamine is a non-AB rated drug.

Another example, if the physician writes a prescription for Salex cream, the pharmacist may dispense the therapeutic alternative to Salex cream, which is Salicylic Acid cream. But, before dispensing Salicylic Acid cream, the pharmacist should call the physician in order to ask for permission because Salicylic Acid is a non-AB rated drug.